Vehicles may be fitted with evaporative emission control systems such as onboard fuel vapor recovery systems. Such systems capture and prevent release of vaporized hydrocarbons to the atmosphere, for example fuel vapors generated in a vehicle gasoline tank during refueling. Specifically, the vaporized hydrocarbons (HCs) are stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel. The fuel vapor recovery system may include one more check valves, ejectors, and/or controller actuatable valves for facilitating purge of stored vapors under boosted or non-boosted engine operation.
Various approaches have been developed for detecting undesired fuel vapor evaporative emissions and/or degraded components in such fuel vapor recovery systems. However, the inventors have recognized several potential issues with such methods. The inventors have recognized that, in particular, it may be difficult to diagnose one or more check valves positioned in the evaporative emissions control system, during vehicle operation under boosted or non-boosted conditions. For example, under non-boosted conditions (e.g., natural aspiration), it may be difficult to determine if a first check valve positioned downstream of a canister purge valve (CPV) and upstream of an intake manifold of the engine is stuck closed, or if gross undesired evaporative emissions (e.g., orifice diameter of 0.04″ or greater) are present in the evaporative emissions control system. Furthermore, under boosted conditions, it may similarly be difficult to determine if a second check valve positioned downstream of the CPV and upstream of an ejector and intake passage, is stuck closed, or if gross undesired evaporative emissions are present in the evaporative emissions control system. More specifically, a stuck closed first check valve may be incorrectly interpreted as gross undesired evaporative emissions under non-boosted conditions. Alternatively, under boosted conditions, gross undesired evaporative emissions may be incorrectly interpreted as a stuck closed second check valve.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example a method is provided, comprising evacuating a fuel system, including a fuel tank that supplies fuel to an engine, and an evaporative emissions system, including a fuel vapor storage canister for storing vapors from the tank, under a first condition and a second condition during a single drive cycle; and diagnosing a plurality of fuel system and evaporative emissions system components based on a vacuum level reached during both the first and second conditions.
As one example, the first condition may include pressure in an intake manifold of the engine less than barometric pressure, and the second condition may include pressure in the intake manifold of the engine greater than barometric pressure. As such, evacuating the fuel system and evaporative emissions system may include communicatively coupling the fuel system and evaporative emissions system to the intake manifold of the engine in the first condition, and communicatively coupling the fuel system and evaporative emissions system to an ejector in an ejector system of the vehicle, where the ejector functions to generate negative pressure in the fuel system and evaporative emissions system, in the second condition. Evacuating the fuel system and evaporative emissions system may further include sealing the fuel system and evaporative emissions system from atmosphere in both the first condition and the second condition.
In some examples, communicatively coupling the fuel system and evaporative emissions system to the intake manifold in the first condition, and communicatively coupling the fuel system and evaporative emissions system to the ejector in the second conditions may further include commanding open a canister purge valve positioned downstream of the fuel vapor canister, and upstream of both the ejector and the intake manifold of the engine. Furthermore, communicatively coupling the fuel system and evaporative emissions system to the intake manifold in the first condition may include opening a vacuum-actuated first check valve positioned upstream of the intake manifold, and communicatively coupling the fuel system and evaporative emissions system to the ejector in the second condition includes opening a vacuum-actuated second check valve positioned upstream of the ejector. As such, diagnosing the plurality of fuel system and evaporative emissions system components based on the vacuum level reached during both the first and second conditions may include diagnosing both the first check valve and the second check valve.
Specifically, responsive to the vacuum level reaching a predetermined threshold vacuum level in the first condition, a first check valve may be indicated to not be stuck closed, and responsive to the vacuum level reaching the predetermined threshold vacuum level in the second condition, the second check valve may be indicated to not be stuck closed. In another example, responsive to the vacuum level reaching the predetermined vacuum level in only one condition, it may be indicated that one check valve is stuck closed, and it may be further indicated that there is an absence of gross undesired evaporative emissions in the fuel system and evaporative emissions system. In other words, responsive to the vacuum level reaching the predetermined vacuum level in at least one of the first condition and the second condition, an absence of gross undesired evaporative emissions in the fuel system and evaporative emissions system may be indicated. However, responsive to the vacuum level reaching the predetermined vacuum level in only one condition, it may be indicated that one check valve is stuck substantially closed. In this way, by evacuating the fuel system and evaporative emissions system under both the first condition and the second condition in a single drive cycle, both the first check valve and the second check valve, along with the presence or absence of undesired evaporative emissions, may be indicated. Specifically diagnosing the check valves and the fuel system and evaporative emissions system may thus lead to reduced undesired evaporative emissions and improved engine operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.